The present invention relates to a buckle for vehicle safety belt systems provided with a pretensioner engaging the buckle.
Buckles for safety belt systems are known in a great many different versions. In one configuration, which has become popular, the load-bearing base of the buckle has an insertion path for the tongue of the belt and a latch slidably guided or swivably mounted on the base transversely to the insertion path to interact with a detent opening of the tongue. A locking member slidably guided parallel to the insertion path in the base holds the latch in its latched position as long as the release button, which is also slidably guided parallel to the insertion path on the base, is in its rest position. This release button is coupled to the locking member, to move it, when actuated, to a release position in which the latch releases from the detent opening of the tongue.
Using such a lock in safety belt systems having a pretensioner is no problem when the pretensioning force engages, for example, on the belt retractor. Pretensioners have also been proposed which are effective between the buckle and its fastening point on the vehicle body or a vehicle seat. Pretensioners of this kind shorten the distance between the fastening point of the buckle and the buckle itself by a few centimeters, for example 10 cm.
The force required for pretensioning can be produced mechanically by means of strongly dimensioned spring or pyrotechnically. If the pretensioning force is sufficiently high, particularly when pyrotechnical pretensioning drive means are used, it may occur in certain cases that the buckle automatically opens at the beginning or at the end of the pretensioning stroke.
Automatic opening of the buckle as a consequence of the pretensioning stroke is attributed to the mass inertia of the release button and of any components acting thereon. For example, at the end of its pretensioning stroke, the release button tends to continue its movement in the pretensioning direction corresponding to the operating direction of the release button.
One way of counteracting a continued movement of the release button under the effect of the forces of inertia is to provide a locking pawl which under the influence of its mass inertia is movable transversely to the direction of pretensioning and which at the end of a pretensioning stroke, when the buckle is abruptly decelerated, assumes a position in which it prevents further movement of the release button in to its release position. A buckle designed on the basis of this principle is disclosed, for instance, by U.S. Pat. No. 5,097,571. Activation of the locking pawl involves a movement of the release button in the direction of the release position; accordingly, the release button must implement some idle travel. The locking pawl prevents the release button from being shifted into the release position. It must be ensured that the locking pawl obtains its locking position before the release button moves past the point at which locking by means of the locking pawl is no longer possible. This requirement restricts the freedom of selecting and dimensioning components for the buckle.
Other known means of counteracting movement of the release button on a pretensioning stroke consist in using compensating inertial bodies, however, this is often disqualified, particularly when space availability is limited.